This invention relates to an apparatus for use during the production of multifilament, synthetic yarn. In particular, it relates to a muffler for use in conjunction with a yarn treating jet for the continuous fluid treatment of running ends of yarn. The jet has at least one yarn passage therethrough and fluid conduits in communication with each of the yarn passages for delivery of the treating fluid.
Throughout the present specification and claims, the term "dB(A)" (decibels -- A-weighted) connotes a unit of measurement of sound level corrected to the A-weighted scale, as defined in ANSI SI.4-1971, using a reference level of 20 micropascals (2.times.10.sup.-5 Newtons per square meter). The term ".DELTA.dB(A)" refers to the difference between two noise levels where each level is expressed in units of dB(A). The term "yarn" is employed in a general sense to indicate strand material, either textile or otherwise, and including a continuous, often plied, strand composed of fibers, filaments, glass, metal, asbestos, paper, or plastic, or a noncontinuous strand such as staple, and the like. An "end" is one or a contiguous group of such strands of yarn. The treating fluid to be used may be virtually any gas, as for example air, steam, nitrogen, oxygen, or carbon dioxide.
The invention is applicable to many phases of yarn handling, the particular use disclosed herein being merely illustrative and not limiting thereof.
Jets have become widely used in recent years for the treatment of industrial and textile yarns. Different jets are used for the various end uses with specific designs having been developed according to the yarn treatment to be effected. Fluid jets have been utilized for such diverse yarn treating operations as entangling, conveying, twisting, crimping, fluffing, localizing the draw point, or otherwise agitating or treating the yarn by means of treating fluid.
All of these jets utilize a fluid which may issue therefrom at high speeds and pressures creating an extremely high noise level. The problem may be further compounded when the treatment comprises a series of fluid treating jets and/or when a plurality of treatment positions are operated simultaneously. The type of muffling device to be employed obviously depends on where the noise issues from the jet. In a fluid treating jet which has a yarn passage therethrough and fluid conduits in communication therewith, the high velocity of the treating fluid jetting out of the fluid conduit into the yarn passage shears into the ambient air thereby creating noise producing turbulent eddies. The cant and direction of the fluid conduits with respect to the yarn passage determines the primary area or areas of noise issuance from the jet. For instance, a treating jet having a fluid conduit at a relatively small angular cant from the yarn passage and directed toward the exhaust end of the yarn passage will have noise issuing primarily from its exit end; this is due to the aspirating effect of the yarn passage with respect to the high velocity air which acts as an impedance to sound waves issuing from the entrance end. However, a treating jet having a fluid conduit approaching more nearly a 90.degree. cant from the yarn passage will have noise issuing more equally from its entrance and exit ends; the jet of treating fluid interacts with the yarn passage to propagate noise in both directions, there being no impedance to sound waves issuing from the entrance end. An increasing angular cant of the fluid conduit from the yarn passage will result in a decreasing aspirating effect and accordingly, in progressively more noise issuing from both ends. Also, if the yarn passage has an adjacent access slot, noise will issue therefrom.
There are various muffling devices known in the art for reduction of noise issuing from a yarn treating jet. There are basically three types of muffling devices or combinations thereof: access slot silencers; entrance or exhaust mufflers; and jet enclosures.
There are several devices in the art for sealing of the access slot. U.S. Pat. No. 3,296,679 relies upon the slideability of a closure plate and gravity to seal the access slot of a fluid treating jet. U.S. Pat. No. 3,905,075 discloses a noise reduction and heat direction system wherein actuating means trips the pivot of noise damping means to cause a wedge to seal the access slot. Both of U.S. Pat. Nos. 3,363,294 and 3,394,440 rely upon fluid actuated movement of either the housing or closure means within the housing for the alignment or misalignment of yarn receiving slots during string-up and operation, to thereby accomplish the automatic sealing of an access slot by fluid operation of the jet. Although access slot silencers of the aforementioned types are effective, the blocking of the access slot alone simply means that the directivity pattern of noise radiation has been changed, i.e., the noise will radiate in a different direction, for instance through the jet entrance and/or exhaust.
There are also several devices in the art which muffle noise issuing primarily from the entrance or exit ends of a yarn treating jet. U.S. Pat. No. 4,043,008 discloses an exhaust muffler which has a hinged door operating in conjunction with an access slot silencer to lower the overall noise level of a yarn treating jet during operation. U.S. Pat. No. 3,127,729 discloses a jet muffler shroud which substantially encloses the exit from a yarn treating jet. Another exhaust muffler is taught by U.S. Pat. No. 4,030,651, for use in conjunction with an interfloor tube aspirator. Another aspirator muffler is disclosed by U.S. Pat. No. 4,024,698, but this is primarily an inlet muffler. Although entrance or exhaust mufflers of the aforementioned types are effective, it is highly desirable to have a muffler which will effectively attenuate noise regardless of the primary source, when dealing with yarn treating jets. Assuming that redesigning the yarn treating jet is not feasible, the best approach is enclosure.
The jet enclosure concept is also known. U.S. Pat. No. 3,713,509 teaches a textile interlacing apparatus which is surrounded with a sound proofing chamber coupled with muffled exhaust ports. U.S. Pat. No. 3,167,847 discloses an improved yarn intertwining jet which includes a blanket of sound insulating or absorbing material overlying the entire exposed surface of its housing and surrounding the operating zone; the coverplate to the housing also has sound absorbing material thereon. U.S. Pat. No. 3,305,910 teaches yarn diverting apparatus which is located in an acoustical enclosure.
The actual sound absorbing materials disclosed by these patents are high porosity low density structures (U.S. Pat. No. 3,713,509); ridid sound absorbing material such as glass fibers (U.S. Pat. No. 3,127,729); foam rubber felt, or porous plastics (U.S. Pat. No. 3,167,847); and completely metal sound absorbing inserts (U.S. Pat. No. 4,043,008).
The primary problem in designing a jet enclosure type of muffler is the inherent conflict between acoustical objectives and process objectives. Acoustically, it is desirable to enclose as much of the jet as possible; however, from a process point of view it is desirable to have no impedance to the yarn path at all. It is impossible to completely enclose a yarn treating jet as the running length of yarn must have some means provided for access to the jet. Provision of large openings or slots (see U.S. Pat. No. 3,305,910) in the enclosure for yarn passage is acoustically undesirable as noise will escape therefrom. However, restricting the openings to a very small size in an enclosure formed of a nonpliable material (see U.S. Pat. No. 3,713,509) may cause regeneration of noise; the high velocity of air issuing from the jet will shear across the edge of the small opening to create more noise. Another problem associated with such small openings is the increased risk of yarn to metal contact, which is undesirable from a process point of view (see U.S. Pat. No. 3,167,847).
Applicants have surprisingly developed a jet enclosure type of muffler which solves the aforementioned problems. Additionally, the design of the present invention is such that the functional life of the sound absorbing material is increased.